Process of submerged nozzle continuous casting using a basalt flux

ABSTRACT

A process of submerged nozzle continuous casting wherein there is used, as a flux layer on the upper surface of the molten metal in the casting mould, a flux composition including the mineral basalt.

United States Patent Austin 51 July 18,1972

PROCESS OF SUBMERGED NOZZLE CONTINUOUS CASTING usmc A BASALT FLUX George Wesley Austin, Nechells, England Foseco International Limited, Birmingham, England Sept. 28, 1970 lnventor:

Assignee:

Filed;

Appl. No.:

Foreign Application Priority Data Oct. 10, 1969 Great Britain ..49,929/69 US. Cl ..164/73, 164/82, 75/94, 164/55 Int. I 822d 11/10 Field ofSearch 164/55, 56, 73, 82, 72, 281;

Primary Examiner-J. Spencer Overholser Assistant Examiner-John E. Roethel Attorney-Wolfe, Hubbard, Leydig, Voit & Osann, Ltd.

[ ABSTRACT A process of submerged nozzle continuous casting wherein there is used, as a flux layer on the upper surface of the molten metal in the casting mould, a flux composition including the mineral basalt.

8 Claims, No Drawings This invention relates to the submerged nozzle continuous casting of metals, particularly steel.

in submerged nozzle continuous casting, molten metal is tecmed from a tundish via a noule into a mould, usually of copper and water cooled, from the base of which a solidified strand of metal is continuously withdrawn. The base of the nozzle is below the level of molten metal in the mould. In order to facilitate the passage of the solidifying strand through the mould, especially when the metal has a high melting point, for example steel, it is customary to provide a lubricant between the molten metal and solidifying strand and the walls of the mould.

The choice of a lubricant is not without considerable difficulty, especially for steel casting. One class of lubricants which has been used are unsaturated fatty oils, in particular rape and crambe oils. These materials, however, are in short supply, expensive and do not give an optimum lubrication. Alteration of their properties to suit the metal and casting temperature is not easy.

A further class of lubricants which are widely used are fluxtype materials which melt to give a glaze-like. lubricant. Typical of these are blast furnace slag, fly ash and high softening point glasses. These may be matched to the metal and casting temperature by the addition of fluorides, but this introduces an undesirable health hazard from the fluorine-containing fumes produced in use. The glass types also present, in crushed form, a silicosis hazard. A further disadvantage of the flux types of lubricant is the variability of the materials from one batch to the next, both in terms of melting point, and lubricating efficiency. However, these lubricants have an advantage over the fatty oils in that they are cheaper and that they can be used so as to form a pool of cleansing and refining slag above the solidifying metal.

In submerged nozzle continuous casting, it is also necessary, in order to prevent the static surface of the molten metal solidifying, to provide a heat insulating cover. Known flux type lubricants, however, do not act efficiently as a heat insulating cover on the metal surface. The flux cover, in addition to heat insulation, should also act as a barrier to surface oxidation of the molten metal. These features are all necessary in order to obtain a continuously cast strand of metal which is of high quality and substantially free from defects such as non-metallic inclusions, laps, ripples and cracks.

It has now been found that covering flux compositions of particular effectiveness and of satisfactory heat-insulation ability may be formulated using the mineral basalt as one ingredient.

According to the present invention, there is provided a process of submerged nozzle continuous casting wherein there is used, as a flux layer on the upper surface of the molten metal in the casting mould, a flux composition including the mineral basalt to an extent of 40-80 percent by weight.

Preferably the flux composition consists substantially of basalt, one or more fluxing agents (e.g. sodium carbonate, calcium fluoride) and blast furnace slag. Particularly preferred fluxes contain about equal weight proportions of basalt and blast furnace slag. The proportion of fluxing agent if included is preferably up to 10 percent by weght.

Other materials which may be present in the composition include perlite and vermiculite, preferably in an amount of l-l percent by weight. These greatly enhance the heat-insulation ability of the flux cover, as well as being of value in the flux composition. It is preferred that in such a composition the particle size of the perlite or vermiculite is all between 0.15 mm and 0.075 mm.

Carbon may also be present in the flux composition to enhance its heat insulative properties by hindering the tendency of the other components of the flux composition to sinter together. The proportion of carbon, if included, is preferably up to percent by weight.

The proportion of blast furnace slag, if included in the flux composition, is preferably 30-50 percent by weight.

Basalt is a widely distributed plentiful mineral which is cheap and not subject to great variation. Generally, basalt softens at about 1,000" C and becomes sufliciently fluid at about 1,500" C to act as an excellent flux for casting steel. Molten basalt is a good solvent for iron oxides and acts well as a lubricant.

Preferably, all the ingredients in any particular flux composition have about the same melting range. This ensures that in use the composition stays as a heat insulating powder until it reaches a high temperature as it approaches the molten metal surface, and that melting is uniform throughout.

The particle size of all components in the flux composition is preferably mostly 0.15 mm to 0.05 mm.

The application rate of the flux composition to the molten metal may vary widely but is usually from 0.5 to 1.5 kg/tonne of metal cast.

It is found that by the process of the present invention, longitudinal surface cracking in the continuously cast slabs is substantiallyeliminated.

The following examples will serve to illustrate the invention:

EXAMPLE 1 A flux composition was made up of, by weight blast furnace slag crushed basalt calcium fluoride perlite (all 0.15 mm to 0.075 mm) 5% EXAMPLE 2 A flux composition was made up of, by weight blast furnace slag 42.5% crushed basalt 42.5% calcium fluoride 5% perlite (all 0.15 mm to 0.075 mm.) 5% carbon 5% This composition was tested in similar fashion to that' described in Example 1, but at an addition rate of only 0.5 kgltonne. Similarly high-quality results were obtained.

lCLAlM AS MY INVENTION:

1. In the process of submerged noale continuous casting wherein there is used as a flux layer on the upper surface of the molten metal in the casting mould, the improvement which comprises using a flux composition including, to an extent of 40-80 percent by weight, the mineral basalt.

2. A process according to claim 1 wherein the flux composition consists substantially of basalt,up to 10 percent by weight of at least one fluxing agent, and up to 50 percent by weight of blast furnace slag.

3. A process according to claim 2 wherein the fluxing agent is selected from the class consisting of sodium carbonate and calcium fluoride.

4. A process according to claim 1 wherein the flux composition contains up to 10 percent by weight of carbon.

5. A process according to claim 1 wherein the flux composition contains l-lO percent by weight of a material selected from the class consisting of vermiculite and perlite.

6. A process according to claim 5 wherein the said material is all of particle size 0.15 mm to 0.075 mm.

7. A process according to claim 2 wherein the blast furnace slag is present in a proportion of 30-50 percent.

8. A process according to claim 1 wherein the flux composition is used at a rate of 0.5 1.5 kg/tonne of metal cast. 

2. A process according to claim 1 wherein the flux composition consists substantially of basalt,up to 10 percent by weight of at least one fluxing aGent, and up to 50 percent by weight of blast furnace slag.
 3. A process according to claim 2 wherein the fluxing agent is selected from the class consisting of sodium carbonate and calcium fluoride.
 4. A process according to claim 1 wherein the flux composition contains up to 10 percent by weight of carbon.
 5. A process according to claim 1 wherein the flux composition contains 1-10 percent by weight of a material selected from the class consisting of vermiculite and perlite.
 6. A process according to claim 5 wherein the said material is all of particle size 0.15 mm to 0.075 mm.
 7. A process according to claim 2 wherein the blast furnace slag is present in a proportion of 30-50 percent.
 8. A process according to claim 1 wherein the flux composition is used at a rate of 0.5 - 1.5 kg/tonne of metal cast. 